Phosphorylation Regulates KSR1 Stability, ERK Activation, and Cell Proliferation

Razidlo, Gina L.; Kortum, Robert L.; Haferbier, Jamie L.; Lewis, Robert E.

doi:10.1074/jbc.m406395200

Cited by 69 publications

(58 citation statements)

References 45 publications

(61 reference statements)

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“…Reconstitution experiments of KSR1 knockout cells with increasing amounts of transfected KSR1 showed that ERK activation became maximal when KSR1 was overexpressed ϳ14 fold above endogenous levels. However, even under these optimal conditions Ͻ5% of MEK and ERK were bound to KSR1 (30). This example shows that even small changes in the efficiency of an activation step within the Raf-MEK-ERK kinase cascade can translate into a strong effect on ERK activity.…”

Section: Discussionmentioning

confidence: 99%

Regulation and Role of Raf-1/B-Raf Heterodimerization

Rushworth

Hindley

O’Neill

et al. 2006

Molecular and Cellular Biology

368

362

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The Ras-Raf-MEK-extracellular signal-regulated kinase (ERK) pathway participates in the control of many fundamental cellular processes including proliferation, survival, and differentiation. The pathway is deregulated in up to 30% of human cancers, often due to mutations in Ras and the B-Raf isoform. Raf-1 and B-Raf can form heterodimers, and this may be important for cellular transformation. Here, we have analyzed the biochemical and biological properties of Raf-1/B-Raf heterodimers. Isolated Raf-1/B-Raf heterodimers possessed a highly increased kinase activity compared to the respective homodimers or monomers. Heterodimers between wild-type Raf-1 and B-Raf mutants with low or no kinase activity still displayed elevated kinase activity, as did heterodimers between wild-type B-Raf and kinase-negative Raf-1. In contrast, heterodimers containing both kinase-negative Raf-1 and kinase-negative B-Raf were completely inactive, suggesting that the kinase activity of the heterodimer specifically originates from Raf and that either kinase-competent Raf isoform is sufficient to confer high catalytic activity to the heterodimer. In cell lines, Raf-1/B-Raf heterodimers were found at low levels. Heterodimerization was enhanced by 14-3-3 proteins and by mitogens independently of ERK. However, ERK-induced phosphorylation of B-Raf on T753 promoted the disassembly of Raf heterodimers, and the mutation of T753 prolonged growth factor-induced heterodimerization. The B-Raf T753A mutant enhanced differentiation of PC12 cells, which was previously shown to be dependent on sustained ERK signaling. Fine mapping of the interaction sites by peptide arrays suggested a complex mode of interaction involving multiple contact sites with a main Raf-1 binding site in B-Raf encompassing T753. In summary, our data suggest that Raf-1/B-Raf heterodimerization occurs as part of the physiological activation process and that the heterodimer has distinct biochemical properties that may be important for the regulation of some biological processes.

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Section: Discussionmentioning

confidence: 99%

Regulation and Role of Raf-1/B-Raf Heterodimerization

Rushworth

Hindley

O’Neill

et al. 2006

Molecular and Cellular Biology

368

362

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show abstract

“…To further substantiate the above observation, we examined the phosphorylation status of ERK in both the cell lines. ERK (or p42/44MAPK) is phosphorylated by the sequential activation of RAF1 and MEK1/2, thereby inducing cell survival and proliferation (Razidlo et al 2004). It has been reported that ERK signaling downregulates the expression of anti-apoptotic proteins and promotes survival of pancreatic cancer cells (Boucher et al 2000).…”

Section: Alteration In Expression Of Cyclin D1 By High Glucose and Inmentioning

confidence: 99%

High glucose and insulin differentially modulates proliferation in MCF-7 and MDA-MB-231 cells

Gupta

Tikoo

2013

Journal of Molecular Endocrinology

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Various preclinical and clinical studies have linked diabetes and breast cancer, but little is known regarding the molecular mechanism involved. This study aimed to investigate the effect of high glucose and insulin in breast cancer cells (MCF-7: non-invasive, hormone dependent, and MDA-MB-231: invasive, hormone independent). In contrast to MCF-7 cells, high glucose augmented proliferation of MDA-MB-231 cells as observed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and bromodeoxyuridine assays. The high-glucose condition led to increased expression of cyclin D1, de-phosphorylation of p38, and increased phosphorylation of ERK in MDA-MB-231 cells but not in MCF-7 cells. Interestingly, we observed increased phosphorylation of GSK-3b, NF-kB, and ERa only in MCF-7 cells, highlighting their role as potential targets in prevention of progression of breast cancer under a high-glucose and insulin condition. Furthermore, insulin treatment under a high-glucose condition resulted in increased histone H3 phosphorylation and de-acetylation only in MDA-MB-231 cells. Taken together, we provide the first evidence that high glucose and insulin promotes proliferation of MDA-MB-231 cells by differential alteration of GSK-3b, NF-kB, and ERa expression and histone H3 modifications, which may directly or indirectly modulate the expression of genes involved in its proliferation.

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“…9,10 In vivo, deletion of Ksr1 inhibits Ras signaling-dependent tumor development in the mammary gland and skin. 8,11 However, there are incongruous data that Ksr1 can promote fibroblast proliferation, 12 but also that deletion of Ksr1 increases spontaneous immortalization and RasV12-induced proliferation of fibroblasts. 10 Therefore, Ksr1 has a critical function in modulating Ras pathway signaling, but its role in the cellular processes linked to transformation and in tumorigenesis remain incompletely resolved.…”

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confidence: 99%

Suppression of Ras/Mapk pathway signaling inhibits Myc-induced lymphomagenesis

Gramling

Eischen

2012

Cell Death Differ

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Although the Myc transcription factor has been shown necessary for the oncogenic function of Ras, the contribution of Ras pathway signaling to the oncogenic function of Myc remains unresolved. We report the novel findings that Myc alone induced Ras/Mapk pathway signaling, and increased signaling following growth factor stimulation. Deletion of the scaffold protein kinase suppressor of Ras 1 (Ksr1) attenuated signaling through the Ras/Mapk pathway, including activation following Myc induction. B cells that lacked Ksr1 exhibited reduced proliferation and increased cytokine deprivation-induced apoptosis. Overexpression of Myc rescued the proliferation defect of Ksr1-null B cells, but loss of Ksr1 increased sensitivity of B cells to Myc-induced apoptosis. Notably, there was a significant delay in lymphoma development in Ksr1-null mice overexpressing Myc in B cells (El-myc transgenic mice). There was an elevated frequency of p53 inactivation, indicative of increased selective pressure to bypass the p53 tumor suppressor pathway, in Ksr1-null El-myc lymphomas. Therefore, loss of Ksr1 inhibits Ras/Mapk pathway signaling leading to increased Myc-induced B-cell apoptosis, and this results in reduced B-cell transformation and lymphoma development. The c-Myc transcription factor is an oncoprotein that is frequently overexpressed in hematological malignancies through translocations, amplifications, and other less characterized mechanisms. Overexpression of Myc, which drives cell cycle progression, is a well-characterized initiating step in human Burkitt's lymphoma, a non-Hodgkin's B-cell lymphoma. The role of Myc in non-Hodgkin's B-cell lymphoma was established in part by the Em-myc transgenic mouse model that overexpresses Myc in B-cells and develops pre-B/B-cell lymphoma. 1 Overexpression of Myc in primary B cells triggers activation of the Arf-Mdm2-p53 tumor suppressor pathway, which leads to apoptosis. Specifically, Myc induces Arf, which inhibits Mdm2, causing p53 activation and B-cell apoptosis. Myc-overexpressing B cells that acquire mutations that inhibit apoptosis survive and can be transformed. This is exemplified in that 80% of the lymphomas that arise in Em-myc mice have deleted Arf, overexpress Mdm2, or have mutated or deleted p53, all of which inhibit Myc-induced apoptosis. 2 Similar observations have been made in human lymphomas. [3][4][5] Therefore, whereas Myc overexpression induces B-cell transformation in vivo, it requires B cells to gain resistance to apoptosis induced by the hyperproliferative signals from Myc for this to occur.The Ras-Raf-Mek-Mapk/Erk (Ras/Mapk) signaling pathway is essential for cell growth, differentiation, and cell survival. 6 Kinase suppressor of Ras 1 (Ksr1) was first identified as a positive modulator of Ras signaling in genetic screens of Drosophila and C. elegans. 7 Subsequent studies have shown Ksr1 functions as a scaffold protein that can bind and facilitate signaling of multiple components of the Ras/Mapk signaling pathway. 6 Deletion of Ksr1 results in decreased Mapk-Erk1/2 ...

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Phosphorylation Regulates KSR1 Stability, ERK Activation, and Cell Proliferation

Cited by 69 publications

References 45 publications

Regulation and Role of Raf-1/B-Raf Heterodimerization

Regulation and Role of Raf-1/B-Raf Heterodimerization

High glucose and insulin differentially modulates proliferation in MCF-7 and MDA-MB-231 cells

Suppression of Ras/Mapk pathway signaling inhibits Myc-induced lymphomagenesis

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